Over 70,000,000 cups of coffee are drunk in the UK a day - 57 per cent of which are supped first thing

But while that 7am might feel like the perfect time for a cuppa, new research questions whether we might all be better off holding off for a little longer.

We tend to produce the most cortisol in the morning. It's the stuff that wakes us up and gets us out of the bed; we all need a certain amount of natural stress (although not too much).

Naturally, our production of the hormone reaches a high at around 8am.

Coffee, rather than increasing our production as a stimulant, actually makes us produce less. If you're having coffee first thing, you're drinking it just when you need your body to produce the most amount of natural stress.

In time, your body starts to rely on caffeine rather than letting cortisol do its job - and that's where caffeine dependence kicks in.

Find that caffeine has no real effect on you? That's probably because you've replaced your natural cortisol with caffeine instead of adding to it - meaning that it has very little effect on your alertness.

Another thing that can make us feel lethargic is having low iron levels.

And a new study by the Scientific Advisory Committee on Nutrition suggests coffee might interrupt your body's ability to properly absorb iron.

You might be better off having a small glass of orange juice with your breakfast instead of a cup of coffee

Speaking on the BBC's Trust Me I'm A Doctor programme, nutrition scientist Professor Paul Sharp from King's College said that consuming coffee with an iron-rich breakfast made it harder for the body to reap the benefits.

That's because coffee is packed full of natural chemicals called polyphenols, which are super efficient at binding to iron and making it less soluble.

Professor Sharp suggests that if you have things like fortified cereals, wholegrain breads, nuts or lean meats and fish for breakfast, you might be better off washing it all down with "a small glass of orange juice or an orange to help increase your iron uptake.

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The best time of day to have a coffee, scientists now say, is between 2pm and 5pm - because that's when your natural cortisol levels start to slide.

Sure, if you're particularly caffeine-sensitive that might be a little late (no one wants to be lying awake at 2am thanks to a late latte), but if you're a regular drinker, it might be worth seeing it makes a difference to your afternoon.

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